Hidden Viruses Slip Past Blood Screening in Southern Mozambique, Study Finds

Blood transfusion remains one of the most consequential interventions in modern medicine, saving lives in surgery, obstetrics, trauma care and the treatment of severe anaemia. Yet every unit of donated blood also carries the potential to transmit blood-borne pathogens if screening fails to detect an infection. In sub-Saharan Africa, where hepatitis B virus (HBV), hepatitis C virus (HCV) and HIV remain endemic, the safety of the blood supply depends on the sensitivity of diagnostic testing and on the composition of the donor population. A new cross-sectional study conducted in the southern Mozambican provinces of Gaza and Inhambane has now provided a detailed picture of both sides of that equation, measuring how often these three viruses appear among donors whose blood had already been approved for transfusion, and estimating the residual risk that infected units could still reach patients.

The research, led by Odete Matola of the Instituto Nacional de Saúde in Mozambique together with colleagues at Universidade Eduardo Mondlane and the Clinton Health Access Initiative, was published in BMC Infectious Diseases. Between December 2022 and February 2024, the team enrolled 3,662 approved blood donors across eight health facilities in the two provinces. Approved donors in this setting are individuals who have passed the routine screening process at a blood bank and whose blood is considered acceptable for transfusion. The study collected sociodemographic information using the ODK Collect digital data tool alongside serological test results for the three viruses, and then subjected plasma samples that had tested negative or indeterminate to a more sensitive molecular assay, the cobas MPX nucleic acid test.

The demographic profile of the donor population reflected patterns common across much of the region. The overwhelming majority of participants, 79.2 percent, were male, and 57.6 percent were between 18 and 29 years old. Most strikingly, 71.9 percent were replacement donors, meaning people who give blood because a family member or friend requires a transfusion, rather than regular volunteer donors who donate altruistically on a recurring basis. This distinction matters epidemiologically: replacement donors are generally considered a higher-risk group because their motivation is situational rather than habitual, they may donate infrequently and under pressure, and they are less likely to have been previously screened or to disclose risk behaviours candidly. International guidance from the World Health Organization has long encouraged health systems to shift toward voluntary non-remunerated donor bases precisely because such donors tend to carry a lower prevalence of transfusion-transmissible infections.

Against that backdrop, the headline seroprevalence figures were comparatively encouraging. Hepatitis B surface antigen, the marker of active HBV infection, was detected in 1.3 percent of donors, corresponding to 44 individuals with a 95 percent confidence interval of 0.9 to 1.7 percent. HIV seroprevalence was likewise 1.3 percent, with 46 donors positive and a nearly identical confidence interval. HCV antibodies were not detected at all, yielding a seroprevalence of 0.0 percent with an upper confidence bound of 0.1 percent. For a region where national population-level HBV prevalence can reach double digits, these numbers suggest that the existing screening cascade at the participating blood banks is intercepting the large majority of infected units before they are released.

However, the study’s most consequential findings emerged from the second layer of testing. When the researchers ran nucleic acid amplification on plasma from samples that had been seronegative or indeterminate, they uncovered a substantial burden of occult infection that routine serology had missed. Among seronegative units, the frequency of HBV positivity was 18.7 per 1,000 blood units, or 46 units in total, with a 95 percent confidence interval of 13.7 to 24.9 per 1,000. HIV was detected in 5.5 per 1,000 units, 14 units, with a confidence interval of 3.0 to 9.3 per 1,000. Even HCV, absent from serology altogether, appeared in 1.2 per 1,000 units, three units, with a confidence interval of 0.2 to 3.5 per 1,000. In other words, despite low observed seroprevalence, the residual risk of transfusion-transmitted infection was high for all three pathogens.

The technical explanation for this gap lies in the biology of these viruses and the limitations of antibody- and antigen-based assays. Serological tests detect the host’s immune response or viral proteins, but there is an inherent window period between infection and the appearance of detectable markers. For HIV, antibodies typically become detectable only weeks after infection; for HCV, the antibody response can lag by several weeks to months. HBV presents an additional challenge in highly endemic areas: individuals with occult hepatitis B infection may carry low levels of circulating viral DNA without detectable surface antigen, particularly in the context of past infection with resolved surface antigenaemia or mutations in the surface antigen gene. Nucleic acid testing (NAT) shortens the window period dramatically by amplifying and detecting viral RNA or DNA directly, often identifying infection days to weeks earlier than serology. The cobas MPX assay used in this study is a multiplex real-time PCR platform capable of simultaneously detecting HIV-1 group M and O, HIV-2, HCV RNA and HBV DNA in pooled or individual plasma samples, which is precisely why it could reveal infections invisible to the frontline serological screen.

The study also quantified the problem of indeterminate results, an underappreciated operational burden in transfusion services. Samples gave indeterminate results for HBV in 3.3 percent of cases, 119 units with a confidence interval of 2.7 to 3.9 percent, for HCV in 2.4 percent, 86 units with a confidence interval of 1.9 to 2.9 percent, and for HIV in 0.2 percent, 7 units with a confidence interval of 0.08 to 0.40 percent. Indeterminate serology can arise from low-level infection, cross-reactive antibodies, sample degradation or assay noise, and each such unit must either be discarded or resolved with confirmatory testing. In a resource-constrained health system, a combined indeterminate rate approaching 6 percent across the three viruses represents a meaningful loss of potentially usable blood and a driver of cost, since every ambiguous result demands repeat testing, molecular confirmation or deferral of the donor.

The implications for transfusion safety in Mozambique are direct. An HBV breakthrough rate of nearly 19 per 1,000 approved units means that, without additional safeguards, roughly one in every 53 units cleared by serology alone could theoretically transmit hepatitis B. The corresponding figures for HIV, 5.5 per 1,000, and HCV, 1.2 per 1,000, are lower but still clinically significant, because even a single transfusion-transmitted HIV infection is a preventable lifelong event. The authors conclude that while seroprevalence among approved donors is low, the residual transmission risk observed for all three pathogens is high, and they call for investment in testing infrastructure, specifically the kind of molecular screening that this study deployed, alongside efforts to strengthen the recruitment and retention of regular volunteer donors. A donor base composed of repeat, voluntarily enrolled individuals who are screened repeatedly over time naturally presents a lower cumulative infection risk than one dominated by first-time replacement donors.

The findings also sit within a broader regional conversation about blood safety. Many low- and middle-income countries still rely primarily on rapid diagnostic tests or enzyme-linked immunosorbent assays for donor screening, because NAT requires capital-intensive laboratory equipment, trained personnel, reliable cold chains and robust sample handling. The Mozambican study, conducted with support from laboratory teams at the Maputo Central Hospital Blood Bank and the Instituto Nacional de Saúde, demonstrates both the feasibility of molecular testing in this setting and the size of the safety gap that exists without it. It also underscores the value of pairing epidemiological surveillance with operational blood bank data: by testing units that had already been approved, the researchers measured the actual residual risk in the supply rather than the theoretical risk in the general population.

For clinicians and policymakers, the study offers a clear evidence base for incremental reform. Expanding NAT coverage, even in pooled-sample formats that reduce per-unit cost, would directly address the HBV and HIV breakthrough infections documented here. Improving the resolution of indeterminate results would recover discarded units and reduce waste. Most fundamentally, building a corps of regular volunteer donors would attack the problem at its source, lowering the entry-level prevalence of infection in the donor pool and making every downstream screening step more effective. As transfusion demand continues to grow with expanding surgical, maternal and paediatric services in southern Africa, the Mozambican data make the case that the safety of the blood supply cannot be judged by seroprevalence alone; the viruses that evade serology are the ones that matter most.

Subject of Research: Seroprevalence and transfusion transmission risk of hepatitis B virus, hepatitis C virus and HIV among approved blood donors in southern Mozambique

Article Title: Seroprevalence and risk of transmission of HBV, HCV and HIV in approved blood donors in southern Mozambique

Article References: Matola, O., Munguambe, A., Loquiha, O., & Mabunda, N. (2026). Seroprevalence and risk of transmission of HBV, HCV and HIV in approved blood donors in southern Mozambique. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14601-y

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14601-y

Keywords: blood donors, HBV, HCV, HIV, seroprevalence, transfusion-transmissible infections, nucleic acid testing, Mozambique, blood safety, replacement donors, occult hepatitis B, BMC Infectious Diseases